Pyongyang retaliates by saying it is examining plan to strike US Pacific territory of Guam

U.S. President Donald Trump has said that North Korea 'will be met with fire and fury like the world has never seen' if it threatened the United States again.

Photograph distributed by the North Korean government shows what was said to be the launch of a Hwasong-14 intercontinental ballistic missile at an undisclosed location in North Korea on July 28th. File photograph: Korean Central News Agency/Korea News Service/AP

US president Donald Trump delivers remarks on North Korea during an opioid-related briefing at his golf estate in Bedminster, New Jersey. Photograph: Jonathan Ernst/Reuters

US president Donald Trump has vowed to respond to North Korea with “fire and fury” if it makes any more threats to attack the United States.

Mr Trump’s comments came after Pyongyang threatened “physical” retaliation for new United Nations sanctions – and on a day fresh evidence emerged that the North Koreans have overcome one of the last major technical obstacles to being able to hit the US or western Europe with nuclear-armed missiles.

“North Korea best not make any more threats to the United States,” Mr Trump told journalists at his club in Bedminster, New Jersey. “They will be met with the fire and the fury like the world has never seen.”

Experts on North Korea have warned that aggressive rhetoric could backfire on its leader Kim Jong-un, convincing him his regime is in imminent jeopardy and triggering what he sees as a pre-emptive attack.

Reuters reported on Tuesday night that North Korea said it was “carefully examining” a plan to strike the US Pacific territory of Guam with missiles. A spokesman for the Korean People’s Army, in a statement carried by the state-run KCNA news agency, said the plan would be “put into practice in a multi-current and consecutive way any moment” once leader Mr Kim makes a decision. In another statement citing a different military spokesman, North Korea also said it could carry out a pre-emptive operation if the US showed signs of provocation.

Nuclear weapon

US intelligence agencies now believe the Pyongyang regime has succeeded in building a nuclear weapon small enough to put on an intercontinental ballistic missile (ICBM), it was reported on Tuesday – a conclusion supported by a Japanese government study.

The US assessment also estimates the North Korean nuclear arsenal has now reached up to 60 warheads, substantially more than earlier assessments.

After two ICBM tests in July, some weapons experts also believe the North Koreans have passed another hurdle, building a reentry vehicle (RV) that can deliver a nuclear warhead back through the earth’s atmosphere so that it explodes on its target.

“I don’t have the slightest doubt that the RVs on these missiles are working,” said Jeffrey Lewis, the director of the East Asia nonproliferation programme at the Middlebury Institute of International Studies at Monterey. “That’s done. We’re there. North Korea can put a nuclear weapon on New York City.”

Other experts are more guarded about the North Korean capabilities, based on the July tests, stressing for example that it is unclear whether the guidance and control issues have been resolved.

As the missiles were tested with much steeper trajectories than would be used in an attack, and because the weight of a warhead is hard to predict, it is hard to estimate the potential maximum range of the weapons. But there is general agreement that if Pyongyang is not already a full nuclear weapons power, it is advancing rapidly towards that goal.

Mixed messages

Before taking office, Mr Trump vowed that North Korea would not develop an ICBM during his presidency. Now that it has happened, the Trump administration has sent mixed messages over how it would respond.

It won a diplomatic victory on Saturday when the UN security council approved a new sanctions package, but the impact of the measures will depend heavily on how far China is willing to go to enforce them.

While the secretary of state, Rex Tillerson, has said the US has no interest in pursuing regime change, the national security advisor, HR McMaster has said that the administration is weighing all options, including a “preventative war”.

Mr Lewis argued it was already too late for that. “The pre- in preventative means ‘before’,” he said. “If you start the preventative war after they have the nuclear ICBM’s, it’s just a regular old nuclear war.”

The US assessment that North Korea has mastered the miniaturization of nuclear warheads was revealed in an internal Defence Intelligence Agency report dated July 28th, according to the Washington Post, which was the first to report on its existence. The report was subsequently confirmed by NBC News.

“The IC [intelligence community] assesses North Korea has produced nuclear weapons for ballistic missile delivery, to include delivery by ICBM-class missiles,” the assessment stated, in an excerpt that was read to The Washington Post.

In its defence white paper, Japan’s government also said Pyongyang’s weapons programme had reached a “new phase”

“It is conceivable that North Korea’s nuclear weapons programme has already considerably advanced and it is possible that North Korea has already achieved the miniaturisation of nuclear weapons into warheads and has acquired nuclear warheads,” the Japanese defence ministry document said.

So far neither the US or Japanese governments have confirmed whether North Korea has built a successful reentry vehicle, and there is disagreement among experts over whether the two recent ICBM tests, on July 4th and 28th, prove.

Michael Elleman of the International Institute for Strategic Studies said that a flash picked up by Japanese weather cameras, suggests that the re-entry vehicle broke apart when it entered the atmosphere.

“These are being called successful tests, but we don’t know how successful they were. We don’t know if it broke up or not, and we don’t know about the accuracy of the system,” Mr Elleman said.

Lewis believes the flash occurred far above the densest layer of the atmosphere and could have been caused by a reflection.

“There is nothing in that video that I can’t see in a successful reentry test done by the Russians,” he said. He said the streaks observed coming from the missile, were “a normal thing to see with a reentry vehicle.”

Reentry vehicle

North Korean state media did not claim the re-entry vehicle survived in the July 28th test, but after the July 4th, it claimed the vehicle “accurately hit the targeted waters without any structural breakdown at the end of its flight”.

The Diplomat online site quoted one source as saying that the re-entry vehicle on the first test survived to an altitude of one kilometre, low enough for an airburst warhead to have a devastating impact over a city.

Scott LaFoy, a Washington-based imagery analyst focusing on ballistic missile and space technologies, said the Japanese report reflected “an increasing belief that North Korea either has or is very close to having a nuclear warhead”.

Based on data and projections by experts at the Middlebury Institute of International Studies, LaFoy told the Guardian: “I lean towards believing North Korea is either in possession of a device, or the potential sixth nuclear test will be the practical test of said device.

The Japanese defence white paper doesn’t add much to this due to its expected government vagueness, but it is consistent with what I’m seeing.”

There is growing concern in Japan over the increasing frequency of North Korean missile tests since Mr Kim became leader in late 2011.

“North Korea’s missiles represent a deepening threat. That, along with China’s continued threatening behaviour in the East China Sea and South China Sea, is a major concern for Japan,” the country’s defence minister, Itsunori Onodera, told reporters in Tokyo.

Japan has held several evacuation drills in recent months in preparation for a North Korean missile attack, while Onodera is among those who have called for the country to acquire the ability to strike North Korean bases if it is attacked.